1. Field of the Invention
The invention relates to a process for arc welding wherein the welding amperage and/or the welding voltage are measured, the measured value for the welding amperage or the welding voltage, respectively, is compared with a predetermined set value for amperage or voltage, respectively, and is altered in case of a deviation of the measured value from the predetermined set value.
In automatic arc welding, it is difficult to maintain the extent of filling the weld seam constant if the cross section of the weld groove, i.e. the groove width and/or depth, is subject to variation. A dimensionally accurate preparation of the workpiece edges is frequently impossible under practical conditions, or entails excessively high manufacturing expenses.
2. Description of the Related Art
It has been suggested to optically detect the degree of filling of the weld groove during arc welding and to change, with the aid of the data determined therefrom, the welding parameters so that a constant extent of filling the weld groove is achieved. However, this method has not as yet achieved practical utilization on account of the difficulties occurring in the optical detection of the degree of filling.
It is furthermore known from Austrian patent No. 362,976 and DOS No. 2,645,788 to measure the welding current in order to control welding installations, and to employ changes in welding current and/or deviations of the latter from a predetermined desired value for the control of weld seams. Heretofore, no disclosures have been directed toward controlling welding installations based on measurement of the welding current in such a way that the degree of filling of weld grooves is maintained at a constant value.
In the arc welding process described in U.S. Pat. No. 4,302,655, the electrode is reciprocated (oscillated) transversely to the weld groove between the workpieces, the welding current and/or the welding voltage being measured at two different points of the reciprocating movement and these values being compared with a precalculated value corresponding to the desired extent of filling. It is moreover set forth in U.S. Pat. No. 4,302,655 that it is conventional to adapt the welding parameters to the groove or, in other words, to regulate the welding parameters in an adapting fashion. These welding parameters are ordinarily the electrode speed, the amperage, the wire feeding speed, the voltage and, in case of oscillation, the amplitude. U.S. Pat. No. 4,302,655 does not contain any suggestion for maintaining the distance of the welding gun from the workpiece at a constant value.
British Laid-Open application No. 2,005,049 describes a process for detecting and optimizing the mechanical properties, such as curvature and/or shape of a weld seam. In this method, inter alia, the spacing between the welding gun and the workpiece and the like is determined and optimized. In British Laid-Open application No. 2,005,049, these mechanical data are detected by sensors. The data detected by the sensors are converted into electrical signals which latter are utilized by way of several intermediate stages for controlling the welding parameters in that they form optimized absolute values for regulating the welding process.
British Laid-Open application No. 2,005,049 proposes to associate the welding gun with a feeler (see left-hand portion of FIG. 2). This feeler is used, inter alia, for measuring the height of the workpieces. Since the feeler is merely intended for picking up the actual height of the workpieces W and W1, British Laid-Open application No. 2,005,049 does not contain any hints, either, to the effect that the welding gun (B.sup.r in the right-hand portion of FIG. 2) is to have a constant distance from the workpieces. Moreover, the suggestion in British Laid-Open application No. 2,005,049 has the drawback that the feeler is located at a spacing from the welding gun so that the feeler cannot carry out its measurements where the welding gun is at a particular point in time.